1. Field of the Invention
The present invention relates to an image forming apparatus including a sensing control system.
2. Discussion of the Background
In recent years, based on the increasing demand for smaller and less expensive configurations, various image forming apparatuses (e.g., copying machines, printers, facsimile machines and multi-function machines) having copying, facsimile and printer functions, have been designed. Accordingly, many of the individual parts, including the sensors, must be made smaller and less expensively. Generally, image forming apparatuses are provided with various kinds of the sensors. In particular, various sensors (e.g. density sensors) are provided around an image carrier, and various sensors (e.g. jam sensors) are provided along a recording medium path.
Japanese Laid-Open Patent Publication No. 6-186801 discloses a reflection type photosensor rotatably supported in the vicinity of (1) a photosensitive device and (2) a transfer belt so that a detecting direction can be varied between the photosensitive device side and the transfer belt side. However, that configuration uses a large space between the photosensitive body and the transfer belt to turn the photosensor and utilizes many parts to mount the photosensor rotatably.
Japanese Laid-Open Patent Publication No. 5-2302 discloses an image forming apparatus having a sensor (21 and 22) fixed inside a transfer means 16. Thus, the optical path of the sensor when sensing a toner pattern on the image carrier 4 and a recording medium is optically “obstructed” by the transfer means. Moreover, the transparency (or amount of obstruction) of the transfer means changes over time due to scratches from friction between the transfer means and the recording medium supported on the transfer means. Thus, a detection error may occur in the sensor because of a change in a quantity of reflected light of the sensor.